A fundamental question in cell biology is how organelles achieve their distinct cytoplasmic localizations. In interphase cells, the Golgi complex is found in close proximity to the microtubule-organizing center (MTOC), on one side of the nuclear envelope. During mitosis, the golgi vesiculates into smaller units which disperse throughout the cytoplasm. At telophase, the vesicles coalesce and return to a pericentriolar location. The long term goal of this research is to elucidate the protein-protein interactions responsible for the specific and cell cycle- regulated, subcellular localization of the Golgi complex. We have shown that isolated Golgi complexes can interact with cytoplasmic components of semi-intact cells, and accumulate in the vicinity of the centrosome. This process requires ATP hydrolysis, the presence of intact microtubules, and is entirely dependent upon the microtubule-based motor, cytoplasmic dynein. The specific aims of the present proposal are to isolate and characterize a potentially novel factor that we have shown is essential for Golgi accumulation at the centrosome. This factor can be released from Golgi membranes by KCI treatment. We wish to determine if this protein acts as a linker to couple the Golgi complex to dynein, and/or microtubules, in a cell-cycle-regulated fashion. This factor has the potential to represent a new class of proteins that can link a molecular motor to a specific membrane-bound organelle.